Method and System for Handling Radio Link Failure in Multi-Rat Dual Connectivity System

1. A method for handling Radio Link Failure (RLF) in a Multiple Radio Access Technology (Multi-RAT) Dual Connectivity (MRDC) system including a User Equipment (UE) connected to a Master Node (MN) and at least one Secondary Node (SN), the method comprising: detecting, by the UE, an RLF with the MN; after detecting the RLF with the MN, determining, by the UE, whether an SN termination condition for terminating a connection with an SN of the at least one SN is met, wherein the SN termination condition comprises receiving a Radio Resource Control (RRC) release message related to the SN at the UE; after detecting the RLF with the MN, initiating, by the UE, an RRC connection re-establishment procedure for the MN and a first timer related to the RRC connection re-establishment procedure for the MN, maintaining, by the UE, the connection with the SN, in response to determining that the SN termination condition is not met; and releasing, by the UE, the connection with the SN, in response to determining that the SN termination condition is met or the first timer being expired, wherein context of the UE is maintained by the MN for a time period longer than a duration of the first timer, after detection of the RLF with the MN.

2. The method of claim 1 , further comprising: continuing, by the UE, data activity with the at least one SN without releasing the connection until the SN termination condition is met.

3. The method of claim 2 , wherein continuing the data activity with the at least one SN comprises: receiving, by the UE, from the MN, information about Data Radio Bearers (DRBs) to be used for continuing the data activity; and continuing, by the UE, the data activity with the at least one SN using the DRBs indicated by the MN.

4. The method of claim 1 , wherein the SN termination condition further comprises at least one of detecting an expiration of a second timer, detecting a stop of the second timer, receiving a re-configuration message at the UE, receiving a new SN configuration, completing an SN data activity at the at least one SN, and detecting an RLF at the at least one SN.

5. A method for handling Radio Link Failure (RLF) in a Multiple Radio Access Technology (Multi-RAT) Dual Connectivity (MRDC) system including a User Equipment (UE) connected to a Master Node (MN) and at least one Secondary Node (SN), the method comprising: detecting, by the MN, an RLF with the UE; after detecting the RLF with the UE, preserving, by the MN, a context of the UE for a particular time period; determining, by the MN, whether an SN termination condition for terminating a connection between the UE and an SN of the at least one SN is met, wherein the SN termination condition comprises receiving a Radio Resource Control (RRC) release message related to the SN at the UE; continuing, by the MN, data activity with the SN until the SN termination condition is met, in response to determining that the SN termination condition is not met; and stopping, by the MN, the data activity with the SN, in response to determining that the SN termination condition is met, wherein after the UE detecting the RLF with the MN, the UE initiated an RRC connection re-established procedure for the MN and a first timer related to the RRC connection re-established procedure for the MN, wherein the MN maintains context of the UE for a time period longer than a duration of the first timer, after detecting the RLF with the UE.

6. The method of claim 5 , further comprising: performing, by the MN, an RLF recovery; determining, by the MN, at least one Data Radio Bearer (DRB) to be used by the UE for continuing the data activity from the UE to the at least one SN while the MN is performing the RLF recovery; and indicating, by the MN, the at least one DRB to the UE associated with the MN.

7. The method of claim 5 , wherein the SN termination condition further comprises at least one of detecting an expiration of a timer, detecting a stop of the timer, receiving a re-configuration message at the UE, receiving a new SN configuration, completing SN data activity at the at least one SN, and detecting an RLF at the at least one SN.

8. A User Equipment (UE) for handling Radio Link Failure (RLF) in a Multiple Radio Access Technology (Multi-RAT) Dual Connectivity (MRDC) system including a Master Node (MN) and at least one Secondary Node (SN), the UE comprising: a transceiver; and at least one processor coupled to the transceiver, wherein the at least one processor is configured to: detect an RLF with the MN, after detecting the RLF with the MN, determine whether an SN termination condition for terminating a connection with an SN of the at least one SN is met, wherein the SN termination condition comprises receiving a Radio Resource Control (RRC) release message related to the SN at the UE, after detecting the RLF with the MN, initiate a first timer and an RRC connection re-established procedure for the MN, maintain the connection with the SN, in response to determining that the SN termination condition is not met, and release the connection with the SN, in response to determining that the SN termination condition is met the first timer being expired, wherein context of the UE is maintained by the MN for a time period linger than a duration of the first timer, after detection of the RLF with the MN.

9. The UE of claim 8 , wherein the at least one processor is further configured to: continue data activity with the at least one SN, without releasing the connection until the SN termination condition is met.

10. The UE of claim 9 , wherein to continue the data activity with the at least one SN, the at least one processor is further configured to: receive, from the MN, information about a Data Radio Bearer (DRB) to be used, for continuing the data activity, and continue the data activity with the at least one SN using the DRB indicated by the MN.

11. The UE of claim 8 , wherein the SN termination condition further comprises at least one of an expiration of a second timer, detecting a stop of the second timer, receiving a re-configuration message at the UE, receiving a new SN configuration, completing SN data activity at the at least one SN, and detecting an RLF at the at least one SN.

12. A Master Node (MN) for handling Radio Link Failure (RLF) in a Multiple Radio Access Technology (Multi-RAT) Dual Connectivity (MRDC) system including a User Equipment (UE) connected to the MN and at least one Secondary Node (SN), the MN comprising: a transceiver; and at least one processor coupled to the transceiver, wherein the at least one processor is configured to: detect an RLF with the UE, after detecting the RLF with the UE, preserve a context of the UE for a particular time period, determine whether an SN termination condition for terminating a connection between the UE and an SN of the at least one SN is met, wherein the SN termination condition comprises receiving a Radio Resource Control (RRC) release message related to the SN at the UE, continue data activity with the SN until the SN termination condition is met, in response to determining that the SN termination condition is not met, and stop the data activity with the SN, in response to determining that the SN termination condition is met, wherein after the UE detecting the RLF with the MN, the UE initiates an RRC connection re-established procedure for the MN and a first timer related to the RRC connection re-established procedure for the MN, wherein the MN maintains context of the UE for a time period longer than a duration of the first timer, after detecting the RLF with the UE.

13. The MN of claim 12 , wherein the at least one processor is further configured to: perform an RLF recovery, determine at least one Data Radio Bearer (DRB) to be used by the UE for continuing the data activity from the UE to the at least one SN while the MN is performing the RLF recovery, and indicate the at least one DRB to the UE associated with the MN.

14. The MN of claim 12 , wherein the SN termination condition comprises at least one of detecting an expiration of a timer, detecting a stop of the timer, receiving a re-configuration message at the UE, receiving a new SN configuration, completing SN data activity at the at least one SN, and detecting an RLF at the at least one SN.